Production method of electronic parts and water treatment apparatus

ABSTRACT

A production method of an electronic part comprising a step o working a substrate having formed thereon a metal thin-film conductor using water, wherein said water satisfies the relations 3.5≦pH≦6.5 and DO≦0.5 pH 2 −6.5 pH+22 [wherein DO represents a dissolved oxygen amount (unit ppm)].  
     By using the water in the case of working substrates in the production steps of electronic parts, the generations of the static electricity and the oxidation caused by water used for working are restrained. The present invention is particularly effective in working of an electronic part wherein a metal thin-film conductor containing at least two kinds of metals including Al on a substrate having a pyroelectric property.

DETAILED DESCRIPTION OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a production method ofelectronic parts having a step of working a substrate having disposedthereon a metal thin film conductor and also to an apparatus forproducing water used in the above-described step.

[0003] 2. Description of the Related Arts

[0004] Hitherto, in the case of working semiconductor substrates, suchas, for example, washing, cutting, polishing, and a surface treatment,water is used. However, when water is sprayed onto a substrate atworking, there is a problem that a static electricity is generatedmainly by the friction between the water and the substrate. That is, inthe case of working a substrate having formed thereon electrodescomposed of a metal thin-film conductor, it sometime happens that theelectrodes are destroyed by the generated static electricity. Recently,because electrodes are fined with small-sizing of electronic parts andincreasing of high integration, the possibility of the destruction ofthe electrodes is more increased. To prevent the occurrence of thedestruction of the electrodes by a static electricity, it is proposed touse an electrically conductive liquid such as a carbonic acidgas-intermixed water, etc., in the case of washing an Si wafer withhigh-pressure water in JP-A-58-7831.

[0005] On the other hand, it is known that when in the case of workingelectronic parts using water, the amount of oxygen dissolved in thewater is large, the electronic parts are corroded and oxidized. Toprevent the occurrence of such a corrosion and oxidation, it is proposedto use a deoxidation water obtained by vacuum deairing via a deoxidationmembrane for washing in JP-A-4-40270. The concentration of oxygendissolved in the deoxidation water is 1 ppm or lower. Also, inJP-A-55-153332, a method of using water which was at least once boiledin the case of washing gallium arsenide semiconductor devices isproposed. The proposition is to prevent the oxidation of a galliumarsenide substrate.

[0006] The above-described propositions are all for the case of usingsemiconductor substrates but recently, electronic parts usingpiezoelectric substrates such as a surface acoustic wave (SAW) element,etc., have been increased. In the case of producing these electricparts, water is used at washing or cutting. However, because in asubstrate having a pyroelectric property such as a piezoelectricsubstrate (for example, LiNbO₃ and LiTaO₃), an electrostatic chargegenerates even by heat and stress, the amount of electrostatic charge isgreatly increased as compared with a semiconductor substrate. Also, inthe electronic parts using piezoelectric substrates, in for example, asurface acoustic wave element, the electrode is thin and fine. In suchcircumstances, in the electronic parts using the piezoelectricsubstrates, particularly, the surface acoustic element, there is aproblem that even when the water having the controlled electricconductivity and dissolved amount of oxygen same as the case ofsemiconductor substrates is used, the electrostatic destruction of theelectrodes cannot be avoided.

[0007] Furthermore, in the surface acoustic wave element, to improve theelectric power resistance, it is proposed to use two or more kinds ofmetals (for example, Al and Cu) for the electrodes but because in suchan electrode, a local cell is formed by the potential difference betweenthe two or more kinds of metals, the influence of the local cell isincreased by the influenced with dissolved oxygen, the corrosion of theelectrode is liable to proceed.

[0008] Also, in an electronic part wherein an metal thin-film conductoris formed on a semiconductor substrate, a protective film made up ofSiO₂, etc., is further formed on the metal thin-film conductor and inthe case of washing or in the case of obtaining plural elements bycutting the substrate, the corrosion of the metal thin-film conductor ishard to occur because the metal thin-film conductor is in the state ofbeing protected with the protective film. On the other hand, in thesurface acoustic wave element, a piezoelectric film is sometimes formedon a metal thin-film conductor but because the metal thin-film conductoris frequently exposed, the resistance to the corrosion is weak.

[0009] Then, by illustrating the production of a surface acoustic waveelement having a metal thin-film electrode containing Al and Cu, thetroubles occurring in the case of working using water are practicallyexplained.

[0010] The troubles occurring at working using water are largely thefollowing 1) to 3).

[0011] 1) Electrode destruction by static electricity (staticdestruction).

[0012] 2) Corrosion of electrodes occurring because the pH of water isoutside a proper range.

[0013] 3) Pitting caused by the action of dissolved oxygen in water asan oxidizing agent.

[0014] The static destruction of 1) occurs when the specific resistanceof water becomes large. Hitherto, the specific resistance of water islowered by dissolving a carbonic acid gas in pure water but because inthe carbonic acid gas dissolving apparatus described in JP-A-58-7831, acarbonic acid gas is intermixed in a bath which is not open to the air,the carbonic acid gas is reluctant to be dissolved in pure water andhence it is difficult to lower the specific resistance of the water.

[0015] The corrosion of the electrode of 2) is caused by the dissolutionof Al occurring when the pH of water is outside the pH range (generally,from 4 to 8) at which, Al can stably exist in the water.

[0016] The pitting of 3) occurs in the pH range (from 4 to 8) at whichAl can stably exist in the water. In an Al—Cu electrode used forimproving the electric power resistance in the surface acoustic waveelement, a passive state (Al₂O₃) film exists on the surface of theelectrode but when a defect exists in the passive state film, a localcell action occurs between Al and CuAl₂ existing in the electrode,whereby Al is dissolved to cause pitting. In the course, dissolvedoxygen becomes one of the factors of proceeding the occurrence ofpitting. In JP-A-58-7831, the specific resistance of water is lowered byintermixing a carbonic acid gas but because in the carbonic acid gasdissolving apparatus described in the above-described patentpublication, the carbonic acid gas is intermixed in a bath which is notopened in the air, the amount of dissolved oxygen in the water cannot berestrained. Thus, it is difficult to use the water produced by theapparatus described in the above-described patent publication for theproduction of surface acoustic wave elements.

SUMMARY OF THE INVENTION

[0017] The present invention has been made under these circumstances. Anobject of the present invention is to restrain the generations of thestatic electricity and the oxidation caused by the water used forworking in the case of working substrates in the production step ofelectronic parts.

[0018] It has now been found that the above-described object can beattained by the invention shown by (1) to (7) described below.

[0019] (1) A production method of an electronic part comprising a stepof working a substrate having formed thereon a metal thin-film conductorusing water, wherein said water satisfies the following relations;

3.5≦pH≦6.5

DO≦0.5 pH²−6.5 pH+22

[0020] [wherein, DO represents the dissolved oxygen amount (unit ppm)].

[0021] (2) A production method of an electronic part of (1) wherein themetal thin-film conductor contains at least two kinds of metalsincluding Al.

[0022] (3) A production method of an electronic part of (1) wherein thesubstrate has a pyroelectric property.

[0023] (4) A water treatment apparatus comprising a mixing bath havingformed an open portion, wherein the mixing bath is constructed such thata carbonic acid gas is intermixed in water to be treated by beingbubbled and dissolved oxygen excluded from the water to be treated withthe intermixed carbonic acid gas is discharged from the open portion.

[0024] (5) A water treatment apparatus of (4) wherein the apparatus hasa water storage tank, the mixing bath has open portions at the upperportion and the lower portion respectively, dissolved oxygen excludedfrom the water to be treated is discharged from the upper open portion,and the carbonic acid gas-intermixed water to be treated is supplied tothe water storage tank from the lower open portion.

[0025] (6) A water treatment apparatus of (4) wherein a carbonic acidgas is supplied to the water to be treated in the mixing bath though aporous filter.

[0026] (7) A water treatment apparatus of (4) wherein the water used inthe production method of an electronic part of (1) is produced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a graph showing the relations of the pH, the specificresistance, and the dissolved oxygen amount of water used for working,and the inferiority generating ratio of a surface acoustic wave elementto be worked.

[0028]FIG. 2 is a cross-sectional view showing an example of thestructure of the water treatment apparatus of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Then, the present invention is described in detail.

[0030] The production method of the present invention has a step ofworking a substrate having formed thereon a metal thin-film conductorusing water. The present inventors determined the relation of the pH andthe dissolved oxygen amount of water and the inferiority generatingratio about a surface acoustic wave element to restrain the inferioritygeneration by working using water. The surface acoustic wave element iscomposed of an LiNbO₃ substrate having formed thereon across-finger-form electrode (thickness 165 nm, electrode finger width 1μm) made up of a 0.5% Cu—Al alloy.

[0031]FIG. 1 shows the relations of the pH, the specific resistance, andthe dissolved oxygen amount (DO) of water, and the inferioritygenerating ratio of the surface acoustic wave element. In addition, DOin FIG. 1 is a dissolved oxygen amount shown by ppm (mg/liter). As shownin FIG. 1, the specific resistance of water changes according to the pH.The inferiority generating ratio shown in FIG. 1 is the generatingratios of both the static destruction and the corrosion of theabove-described electrode. In addition, at the measurement of theinferiority generating ratio, a test of immersing the element in waterfor 24 hours, a test of exposing the element to running water formaximum 6 hours, and a test of high-pressure water spraying imitating adicing (cutting) process were carried out.

[0032] From the experimental results, the inventors have found that byusing water satisfying

3.5≦pH≦6.5

[0033] and

DO≦0.5 pH²−6.5 pH+22

[0034] for working of electronic parts, the inferiority generating ratiocan be remarkably restrained. In addition, even when a carbonic acid gasis dissolved in water until the gas is almost saturated, it is difficultto be the pH of the water lower than 3.5.

[0035] As is clear from FIG. 1 and the above-described relations, withlowering the pH and the specific resistance of water, the allowabledissolved oxygen amount in the water is increased. This has neverhitherto been indicated and has been first clarified by the invention.Accordingly, by applying the present invention, the freedom of thecondition establishment in the production process can be increased. Forexample, because when the dissolved oxygen amount in water is lowered toabout 1 ppm, even when the pH of the water is relatively high as 5, theinferiority generating ratio can be almost completely restrained, thepresent invention is suitable for the case of requiring a relativelyhigh pH of water for prolonging the life of a cutting blade as will bedescribed below. On the other hand, in the case of causing no problemeven when the pH of water is 4, when the dissolved oxygen amount is highas 3 ppm, the inferiority generation can be restrained, whereby the costfor removing dissolved oxygen can be restrained. Also, the water whereinthe pH is about 4 and the dissolved oxygen amount is 3 ppm or lower iseasily obtained by only the water treatment apparatus of this inventiondescribed below without need of other treatment. Accordingly, in thepresent invention, it is preferred to use the water wherein the pH offrom 3.6 to 4.2 and the dissolved oxygen amount of 3 ppm or lower.

[0036] In addition, as mentioned above, the pH range of water, at whichAl used for electrode can stably exist is considered to be 4 or higherbut according to the inventors' investigation, it has been found that byapplying, for example, annealing to an electrode made up of Al or madeup of Al as the main constituent, a strong Al₂O₃ film can be formed onthe surface thereof and thus the water having a pH of 3.5 or higher butlower than 4 can be used.

[0037] Now, to cut an Si wafer, it is general to use a blade formed bybinding diamond grinding stone particles with an Ni-base metal binderbut when water having a pH of about 4 is used, the Ni-base metal binderis corroded and the life of the blade is greatly shortened. In thiscase, by increasing the pH of the water to about 5 and also lowering thedissolved oxygen amount, the life of the blade can be prolonged withoutaccompanied by the inferiority generation. In addition, because in ablade using a phenol resin as the binder, the life thereof is notlowered even when the pH of water to 4, it is suitable in the case ofrequiring a low pH.

[0038] The dissolved oxygen amount may be measured by a general method.That is, for example, a commercially available apparatus utilizing apolarographic system oxygen electrode using platinum as the cathode,silver as the anode, and an alkali solution as the electrolyte or agalvanic system electrode using platinum as the anode, lead as thecathode, and an alkali solution as the electrolyte can be used for themeasurement. In addition, FIG. 1 shows the result obtained using thepolarographic system oxygen electrode. The polarographic system has afeature that the reproducibility is excellent as compared with thegalvanic system.

[0039] In addition, FIG. 1 is the results about a specific surfaceacoustic wave element but according to the inventors' experiments, ithas been confirmed that when the pH of the water used is in theabove-described range and the pH and the DO of the water are in theabove-described relation, about all the electronic parts using asubstrate having a pyroelectric property, the inferiority generatingratio is similarly greatly reduced.

[0040] The present invention can be applied to the productions ofvarious kinds of electronic parts each using a substrate having formedthereon a metal thin-film conductor. The substrate may be one having apyroelectric property such as a piezoelectric substrate, etc., or asemiconductor substrate but because as described above, in an electronicpart wherein a fine metal thin-film conductor pattern is formed on asubstrate having a pyroelectric property, an inferiority is liable tooccur, the present invention is particularly effective for theproduction of such electronic parts.

[0041] As the metal thin-film conductor of an electronic part to whichthe production method of the present invention is applied, there may beone made up of Al or one made up of Al and one or more kinds of othermetals, and in any case, the effects of this invention are realized.However, as described above, the present invention gives particularlyhigh effects to the electronic parts each having a metal thin-filmconductor comprising an alloy or a laminate capable of causing a localcell action. The electrode containing Al and at least one other metal isused for increasing, for example, the electric power resistance in asurface acoustic wave element. Other metals than Al include, forexample, Cu, Ti, Pd, Nb, Sc, Ni, Mg, Ge, Si, Co, Zn, Li, Ta, Au, Ag, Pt,Cr, Hf, Zr, Cd, W, and V. The content of other metal(s) than Al isgenerally not more than 20% by weight. As the metal thin-film conductorcontaining Al and at least one other metal than Al, there may be notonly those of a single layer structure made up of an Al alloy, but alsothose of a structure of laminating two or more kinds of thin layers eachhaving a different composition and those of a structure of, for example,an Al/Cu laminate or repeatedly laminating the laminate. There is noparticular restriction on the thickness of the metal thin-film conductorbut in a cross-finger-form electrode, the thickness is usually fromabout 0.03 to 1.5 nm. Also, the electrode finger width of thecross-finger-form electrode may be properly selected according to thefrequency which is applied to the surface acoustic wave element, and,for example, in the frequency band of from 10 to 500 MHz, the width isgenerally from about 2 to 10 μm.

[0042] There is no particular restriction on the means of making the pHand the dissolved oxygen amount of water the above-described relation inthe present invention. For example, a method of lowering the pH bydissolving a carbonic acid gas as in a conventional method can beutilized. However, as described above, in a conventional carbonic acidgas dissolving apparatus, the dissolution is carried out in a bath of aclosed system. According to the inventors' experiments, in the case ofcarrying out the dissolution of a carbonic acid gas in a bath of aclosed system, lowering of the dissolved oxygen amount is not obtained.Also, it has been found that in the dissolution of a carbonic acid gasin a bath of a closed system, it is difficult to increase the dissolvedamount of a carbonic acid gas. Accordingly, as far as the conventionalapparatus is used, it is necessary to carry out a dissolved oxygenamount reducing treatment independent from the dissolution treatment. Inthis case, for the dissolved oxygen amount reducing treatment, a vacuumremoving method, a boiling method, an application of ultrasonic wave,the use of a disoxidant, the use of a disoxidation membrane, etc., maybe utilized.

[0043] However, when both the dissolution of a carbonic acid gas and thedissolved oxygen reducing treatment are carried out independently,lowering of the productivity and a cost up are accompanied. Thus, in thepresent invention, the water treatment apparatus of carrying outcarbonic acid gas bubbling in a bath of an open system as describedbelow is proposed.

[0044] An example of the structure of the water treatment apparatus ofthis invention is shown in FIG. 2 as the cross-sectional view. The watertreatment apparatus of this invention has the structure that acylindrical mixing bath 3 having the open upper end and the open lowerend is disposed in a water storage tank 2 by thrusting through theclosed upper wall of the storage tank 2. At the upper portion of themixing bath 3 are formed a carbonic acid gas supplying pipe 4 extendingthrough the inside of the mixing bath 3 into the inside of the waterstorage tank 2 and a supplying pipe 5 of water to be treated. At the endportion of the carbonic acid gas supplying pipe 4 disposed in the insideof the water storage tank 2 is formed a porous filter 41. The porousfilter 41 is a membrane filter made up of a resin film having manypores. The porous filter illustrated in the figure is a hollow body andhas a structure that a carbonic acid gas is press-sent in the insidethereof from the carbonic acid gas supplying pipe 4. At the lowerportion of the water storage tank 2 is formed a treated waterdischarging pipe 6 connecting outside. In the water treating apparatus,from a pure water producing apparatus of the outside, water (pure water)to be treated is supplied in the mixing bath 3 through the supplyingpipe 5 of water to be treated and in the water storing course, water tobe treated is bubbled in the mixing bath 3 with the carbonic acid gassupplied through the porous filter 41 existing near the bottom portionof the mixing bath 3. In this case, the carbonic acid gas is dissolvedin the water to be treated to lower the specific resistance thereof andat the same time, dissolved oxygen contained in the water to be treatedis excluded by the carbonic acid gas. Also, the excluded dissolvedoxygen is discharged together with excessive carbonic acid gas from theopen upper portion of the mixing bath 3. The pure water (treated water)of which the specific resistance is lowered and the dissolved oxygenamount is reduced as described above is discharged to the outside theapparatus from the treated water discharging pipe 6 through the waterstorage tank 2 and is supplied to a working apparatus such as asubstrate washing apparatus, a substrate cutting apparatus, etc. Inaddition, in the construction, because the water storage tank 2functions as a buffer tank for buffing the difference between theproduction speed of treated water and the using speed thereof, it isunnecessary to finely control the supplying amount of the water to betreated according to the using amount of the treated water.

[0045] One feature of the apparatus is in that by bubbling a carbonicacid gas in an open-type mixing bath, the carbonic acid gas can bereplaced with dissolved oxygen in water. Another feature of theapparatus is to use the porous filter 41 of the above-describedconstruction. By using a hollow-type membrane filter having many poresand bubbling a carbonic acid gas through the pores, the contact areas ofthe carbonic acid gas and the water to be treated are increased, wherebyit becomes possible to dissolve the carbonic acid gas in the water to betreated until the gas is almost saturated in a short time. To such awater treatment apparatus of this invention, in a conventionalclosed-type carbonic acid dissolving apparatus, the dissolved oxygenamount in water cannot be reduced by the dissolution of a carbonic acidgas and also because in the conventional apparatus, bubbling through theporous filer as described above is not carried out, it is substantiallyimpossible to lower the pH of water to the above-described preferredrange (3.6 to 4.2) unless the treatment speed is extremely lowered.

[0046] By using the water treatment apparatus of this invention asdescribed above, the treated water having a low specific resistance anda less dissolved oxygen amount as compared with those of the water to betreated can be easily obtained by only carbonic acid gas bubbling.Practically, the treated water having pH of about 4 (specific resistanceof 0.03 MΩ·cm) and containing a dissolved oxygen amount of about 3 ppmis easily obtained. Furthermore, the production cost in the apparatususing an open-system bath is greatly low as compared with an apparatususing a closed-system bath. On the other hand, when a conventionalclosed-system bath is used and the treatment speed is same as that ofthe water-treatment apparatus of this invention, the pH of the water islowered only about 5 (the specific resistance of 0.2 MΩ·cm) and thedissolved oxygen amount is about 8 ppm, which is almost same as that inordinary pure water. To lower the dissolved oxygen amount to the samelevel as that in the case of using the water treatment apparatus of thisinvention, it is necessary to independently carry out a dissolved oxygenamount reducing treatment. However, for example, a membrane deaeratorusing a deoxidation membrane is more expensive than an expensiveclosed-system water treatment apparatus.

[0047] In addition, because the replacement efficiency (replacementspeed) of a carbonic acid gas is changed according to various conditionssuch as the pore diameter of the porous filter 41, the amount of asupplying carbonic acid gas, the pressure thereof, the supplying speedof water to be treated, etc., the combination of these variousconditions may be experimentally determined such that the desired pH anddissolved oxygen amount are obtained but the pore diameter (averagediameter) of the porous filter 41, which gives particularly largeinfluences, is preferably not larger than 200 μm, more preferably notlarger than 100 μm, and far more preferably not larger than 50 μm. Bydefining the pore diameter to the above-described size, a sufficientreplacement efficiency of a carbonic acid gas is obtained. However,because if the pore diameter is too small, a high pressure is requiredfor bubbling, it is preferred that the pore diameter is usually 5 μm orlarger.

[0048] Also, the example shown in FIG. 2 is the construction that theupper wall of the water storage tank 2 is closed but even when the upperwall is opened, the influence giving the pH of water is less. However,to prevent falling of impurities and dust into the water storage tank 2,the closed construction as illustrated in FIG. 2 is preferred.

[0049] The water treatment apparatus of the present invention is notlimited to the construction illustrated in FIG. 2. That is, when theapparatus is a water treatment apparatus equipped with a mixing bathhaving formed an open portion, wherein by bubbling a carbonic acid gasin the mixing bath, the carbonic acid gas is intermixed in water to betreated and dissolved oxygen excluded from the water to be treated withthe intermixed carbonic acid gas is discharged from the above-describedopen portion, the effect of this invention is realized. Furthermore,when the apparatus is a construction using a mixing bath having openportions at the upper portion and the lower portion respectively,wherein dissolved oxygen excluded from water to be treated is dischargedfrom the above-described upper open portion and the carbonic acidgas-intermixed water to be treated is supplied to a water storage tankfrom the above-described lower open portion, that is, when a waterstorage tank as such a buffer tank is formed, the above-described effectis realized. Such a buffer tank is not limited to the constructioncontaining a mixing bath in the inside as shown in FIG. 2 but may be aconstruction connected to the lower open portion of the mixing bath by aconnecting pipe, etc.

[0050] When a test of immersing the surface acoustic wave element usedin the experiment of which the results were shown in FIG. 1 in thetreated water produced by the water treatment apparatus of the presentinvention was performed, any inferiority was not generated even when theimmersion was continued for 24 hours. On the other hand, when thetreated water produced by a conventional closed-type water treatmentapparatus was used, the corrosion of the electrode occurred by theimmersion for one hour.

[0051] In the treated water obtained by the water treatment apparatus ofthe present invention, it is considered that the dissolution of acarbonic acid gas is in an almost saturated state and also the changesof the pH and the dissolved oxygen amount with the passage of time areless. For example, when the treated water is stored for one week atnormal temperature and normal pressure, the pH and the dissolved oxygenamount do not substantially change. Accordingly, the water treatmentapparatus of this invention is not limited to the construction that theapparatus is used by being incorporated in a part of a working apparatusas illustrated in FIG. 1 but can be used as an independent watertreatment apparatus.

[0052] In addition, if necessary, the water treatment apparatus of thisinvention using the open-type bath may be used together with theabove-described dissolved oxygen reducing apparatus. Also, when thewater treatment apparatus of this invention is used and other gas suchas N₂ or Ar is bubbled in placed of a part or the whole of a carbonicacid gas, the dissolved oxygen amount only can be effectively reducedwithout lowering the pH too much or without substantially lowering thepH. This method is effective in the case of requiring the use of adevice or a cutting blade, which has a restriction about pH.

[0053] As described above, the present invention has the followingeffects.

[0054] In the present invention, because in the case of workingsubstrates each having on the surface thereof a metal thin-filmconductor using a water, the water wherein the pH and the dissolvedoxygen amount are in a definite relation is used, the occurrence ofinferiority is restrained and also the freedom of the establishment inthe production process is increased.

[0055] The water used for the production method of this invention can beproduced by using a conventional closed-type carbonic acid gasdissolution apparatus together with an independent dissolved oxygenamount reducing apparatus but by using the water treatment apparatus ofthis invention using the open-type mixing bath, the above-describedwater can be produced at a greatly low cost.

What is claimed is:
 1. A production method of an electronic partcomprising a step of working a substrate having formed thereon a metalthin-film conductor using water, wherein said water satisfies thefollowing relations; 3.5≦pH≦6.5DO≦0.5 pH²−6.5 pH+22 [wherein, DOrepresents the dissolved oxygen amount (unit ppm)].
 2. A productionmethod of an electronic part of claim 1 wherein the metal thin-filmconductor contains at least two kinds of metals including Al.
 3. Aproduction method of an electronic part of claim 1 wherein the substratehas a pyroelectric property.
 4. A water treatment apparatus comprising amixing bath having formed an open portion, wherein the mixing bath isconstructed such that a carbonic acid gas is intermixed in water to betreated by being bubbled and dissolved oxygen excluded from the water tobe treated with the intermixed carbonic acid gas is discharged from theopen portion.
 5. A water treatment apparatus of claim 4 wherein theapparatus has a water storage tank, the mixing bath has open portions atthe upper portion and the lower portion respectively, dissolved oxygenexcluded from the water to be treated is discharged from the upper openportion, and the carbonic acid gas-intermixed water to be treated issupplied to the water storage tank from the lower open portion.
 6. Awater treatment apparatus of claim 4 wherein a carbonic acid gas issupplied to the water to be treated in the mixing bath though a porousfilter.
 7. A water treatment apparatus of claim 4 wherein the water usedin the production method of an electronic part of claim 1 is produced.